Process for the preparation of polyalkenyl-substituted succinic anhydride

ABSTRACT

An improved process is disclosed for the preparation of polyalkenyl-substituted succinic anhydride comprising a final thermal treatment after removal of excess maleic anhydride from the reaction mixture, resulting in lowered chlorine content of the desired product.

The invention relates to an improved process for the preparation ofpolyalkenyl-substituted succinic anhydride.

BACKGROUND OF THE INVENTION

It is known from UK Specification No. 1,543,039 to preparepolyisobutene-substituted succinic anhydride (PIB/MALA) by reacting amixture of maleic anhydride and a polymer of isobutene with a molardeficiency of chlorine on maleic anhydride.

The mixture of polymer and maleic anhydride is suitably heated to thereaction temperature before it is contacted with the chlorine. Themixture is contacted with a molar deficiency of chlorine before asubstantial amount, e.g. less than half, of the maleic anhydride hasreacted. Suitably substantially none of the maleic anhydride hasreacted. The rate of introduction of chlorine into the mixture may varybetween wide limits but is preferably such that it equals the rate ofchlorine uptake. Usually the chlorine is introduced over a period offrom 0.5 to 10 hours, preferably of from 3 to 7 hours.

After the chlorination treatment it is advantageous to subject theresultant product mixture to a post-reaction or thermal treatment. Thisthermal treatment is suitably carried out at a temperature in the rangefrom 140° to 220° C., preferably from 160° to 210° C. The conditions areusually such, that substantially no part of the product mixture isremoved during this thermal treatment. The thermal treatment may be forfrom 0.1 to 20 hours but preferably from 0.5 to 10 hours. Longer periodstend to increase the formation of tarry by-products.

Using the above process a conversion of the polymer of isobutene (PIB,molecular weight 1029) of up to 90% is reached whereas the percentage ofchlorine in the product is about 0.4%w. Comparing the above process withother art processed the most striking advantage of the first is that atreaction temperatures of about 200° C. higher polymer conversions tolower chlorine containing products are obtained. These prior artprocesses are described in e.g. published Netherlands Applications No.7412057 and No. 7313404 and in UK Specification No. 949,981.

It is known, e.g. from published Netherlands Application No. 7412057, toprepare polyisobutene-substituted succinic anhydride by reactingthermally a polymer of isobutene with maleic anhydride. From publishedNetherlands Application No. 7313404 it is known to prepare similarproducts by reacting thermally the polymer of isobutene with maleicanhydride until substantially all (i.e. at least half) of the maleicanhydride has been consumed and thereafter continuing the reaction inthe presence of chlorine.

One problem often encoutered with these processes, which involve asubstantial amount of thermal reaction, is that fairly hightemperatures, e.g. temperatures about 220° C., are required to achieve asatisfactory reaction rate and at such high temperatures an undesirableamount of tarry by-products are formed.

From UK Specification No. 949,981 it is known to prepare such productsby containing a mixture of the polymer of isobutene and maleic anhydridewith at least one mole of chlorine for each mole of maleic anhydride(one-stage chlorination route). Since such a process does not involve asubstantial amount of thermal reaction it is possible to use a lowertemperature e.g. a temperature of below 220° C. However, the finalproduct contains a fairly high amount of chlorine.

It is known e.g. from U.S. Pat. Nos. 3,960,889 and 4,000,162 to preparealkylenepolyamine derivatives of the reaction product of adehydrohalogenated polyalkene and maleic anhydride, which derivativesare useful detergent-dispersants in lubricating oil.

It has now surprisingly been found that at high PIB-conversion levels(up to 90%) the chlorine percentage in the product obtained from asimilar process as that described in UK Specification No. 1,543,039 canfurther be decreased to less than 0.2%w if the PIB/MALA Product issubjected to a thermal treatment after excess MALA Has been strippedoff.

SUMMARY OF THE INVENTION

Accordingly the present invention relates to a process for thepreparation of polyalkenyl-substituted succinic anhydride comprisingpreparing a mixture of an alkene polymer and maleic anhydride,contacting the mixture with chlorine at elevated temperature, andremoving excess maleic anhydride, characterized in that after removingexcess maleic anhydride the formed polyakenyl succinic anhydride issubjected to a thermal treatment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Suitably the thermal treatment is carried out at a temperature of from140°-230° C. Preferably the temperature range is from 185-210° C. Thethermal treatment is suitably carried out for from 0.1-30 hours,preferably from 3-6 hours. The pressure at which the thermal treatmentis carried out is suitably of from 10-200 mbar.

Suitably polyolefins for the polyalkenyl succinic anhydride includepolyethylene, polypropylene, polybutenes or mixtures of polybutenes etc.of which polyisobutene is preferred, because of its availability andeffectiveness in the products derived from it. The average molecularweight of the polyalkenyl group is preferably of from 300-200,000.

The products of the present invention are particularly suitable for thepreparation of ashless dispersants for oils such as lubricating oils.These dispersants are prepared by reacting the products, or thehydrolysis products thereof, with polar compounds, such as polyalcohols,e.g. pentaerythritol or tris(hydroxymethyl-amino)methane, and/orpolyamines, e.g. polyalkylene amines such as tetraethylene pentamine.

It has been found that when the present product is reacted withpolyamines e.g. with tetraethylene pentamine the problem of a largeamount of insoluble material formed by the reaction of the polyamineswith HC1 and which has to be removed by filtration is substantiallysolved. This problems appears to exist when higher chlorine percentageproducts are used such as the product prepared by the former mentionedprocess according to UK Specification No. 1,543,039.

The invention therefore also related to a process wherein the polyakenylsuccinic acid is reacted with a polyamine. Preferably tetraethylenepentamine is used.

The invention will now be described by reference to the followingexamples.

EXAMPLE I

A mixture of 660 pbw of a polymer is isobutene (PIB, molecular weight960) and 109 pbw of maleic anhydride (MALA, molar ratio MALA to PIB1.7:1) was heated to 180° C. and purged with nitrogen. Chlorine (52.5pbw, molar ratio of chlorine to MALA 0.67:1) was introduced below thesurface of the mixture during a period of 5 hours. The mixture was thenheated at 180° C. for 4 hours. Then excess MALA was removed. The PIBconversion was 83% while the acid number of the crude product was 1.86meq/g.

The PIB/MALA product containing 0.41%w chlorine was subjected to athermal treatment at 210° C. in a nitrogen stream.

The dehydrochlorination of PIB/MALA was followed by determining thechlorine content at various points of time as represented in the nexttable.

                  TABLE I                                                         ______________________________________                                        Dehydrochlorination of PIB/MALA at 210° C. in a nitrogenstream                Time, h                                                                              Cl, % w                                                         ______________________________________                                               0      0.41                                                                   1      0.30                                                                   2      0.26                                                                   5      0.21                                                                   6      0.21                                                                   8      0.20                                                                   24     0.18                                                            ______________________________________                                    

EXAMPLE II

After 24 hours of thermal treatment at 185° C. under N₂ the PIB/MALAProduct contained 0.26%w chlorine. This product was reacted with tetraethylene pentamine (TEPA) in a ratio of 188 gram TEPA/1000 g PIB/MALAand the deposit calculated on intake of TEPA.

For a comparison the untreated PIB/MALA product, containing 0.41%wchlorine, was also reacted with TEPA in the same ratio and the depositwas calculated. Table II shows the results of this experiment.

                  TABLE II                                                        ______________________________________                                                                 Deposit, % w                                                     g TEPA       calc. on intake                                                  1000 g PIB/MALA                                                                            TEPA                                                 ______________________________________                                        PIB/MALA (0.41 % w                                                            Cl.sub.2) untreated                                                                         188            6.4                                              PIB/MALA (0.26 % w                                                            Cl.sub.2) treated                                                                           188            1.5                                              ______________________________________                                    

As can be seen from the figures in Table II the deposit in case oftreated PIB/MALA is surprisingly about four times less than the depositin case of untreated PIB/MALA, whereas the chlorine content is about twotimes less than the chlorine content of the untreated PIB/MALA. Oneshould expect in view of the ratio in chlorine contents between thetreated and untreated PIB/MALA that the treated PIB/MALA should show adeposit of about two times less than that of the treated PIB/MALA.

What is claimed is:
 1. In a process for the preparation ofpolyalkenyl-substituted succinic anhydride which comprises preparing amixture of an alkene polymer and maleic anhydride, contacting themixture with chlorine at elevated temperature followed by apost-reaction and then removing excess maleic anhydride, the improvementwhich comprises after removing excess maleic anhydride, subjecting theformed polyalkenyl succinic anhydride to a thermal treatment at atemperature of from 140°-230° C. for a period of 0.1 to 30 hours.
 2. Aprocess as in claim 1 wherein the thermal treatment is carried out at atemperature of from 185°-210° C.
 3. A process as in claim 1 wherein thethermal treatment is carried out for from 3-6 hours.
 4. A process as inclaim 1 wherein the thermal treatment is carried out at a pressure offrom 10-200 mbar.
 5. A process as in claim 1 wherein the polyalkenylsuccinic anhydride is a polyisobutenyl succinic anhydride, of which thepolyisobutenyl group has an average molecular weight of from300-200,000.